At the age of 18, Heinz Kuhn becomes a member of SPD. With the National Socialists taking power in 1933, he leaves Germany and begins his journalistic career. In 1946 Kühn comes back and between 1946 and 1950 works as editor-in-chief from the newspaper Rheinische Zeitung.

Heinz Kühn’s political career has different phases: in 1948 he enters the newly formed state Parliament, the Landtag, in North Rhein-Westphalia, and between 1953 and 1963, the Federal Parliament. In 1960 he is chosen second-in-command from SPD and 2 years later, chairman of the party. From 1973 to 1975, the politician is again, second-in-command from SPD.

Heinz Kühn is elected governor of North Rhein-Westphalia in 1966, a position he held until 1978. Due to his leadership qualities, the politician helped the SPD to become the most important political party in the state. Among the main objectives at that time was the administrative boundary revision, educational reforms and improvements in the Ruhr region (coal-mining and steel industry). The social-liberal coalision – SPD and FDP (known as Düsseldorfer Modell), was used, later, as an example of administration to the federal sphere. At the age of 66, Heinz Kühn was still part of German political arena. Between 1978 und 1980 he accepted the position as Commissioner for Foreigners. Within the same period he was elected to take part in the European Parliament.